The present invention generally relates to electrophotography and more particularly, to a rotary type developing apparatus provided with a plurality of developing units for use in an image forming arrangement such as an electrophotographic copying machine and the like.
Commonly, for producing a plurality of single-colored copies each in a different color, it is necessary to replace developing tanks for each color. In a typical image forming arrangement, a plurality of developing tanks are arranged in which developing materials of different colors are respectively accommodated so as to replace one developing tank with another to be actually used by opening a front panel of the image forming arrangement. In the above construction, however, since the number of developing tanks mounted in the main body of the arrangement is limited to only one, there is the disadvantage that the developing tank must inevitably be exchanged for that for changing the color of the copy.
Accordingly, there has conventionally been proposed in Japanese Patent Publication Tokkosho No. 55-3707, a developing apparatus in which a plurality of developing tanks are disposed around a photoreceptor drum so as to make it possible to use any desired developing tank depending on the necessity.
In the above known arrangement, however, a large space is occupied around the photoreceptor drum by the developing tanks, thus adversely affecting other image forming processing members. Furthermore, since the distance from an exposure position to a developing position differs for each developing tank, there is the possibility that tone of color, image contrast, etc. become different according to each developing tank. Moreover, owing to the fact that the angle for development of the developing tank with respect to the surface of the photoreceptor drum is also different for each tank, thus making it necessary to change the shape of the developing tank accordingly, there is also the disadvantage that the manufacturing cost of the developing tanks is increased on the whole.
Japanese Patent Publication Tokkosho No. 46-13478 discloses an image forming arrangement in which a plurality of developing tanks are rotatably supported on the same shaft. In this arrangement, however, a complicated driving mechanism is required since the respective developing tanks are directed in the same direction at all times, with a consequent increase in the size of the arrangement.
Meanwhile, in Japanese Patent Publication Tokkosho No. 55-20579, there has conventionally been proposed a rotary type developing apparatus in which a plurality of developing tanks are rotatably supported for selectively causing one of the tanks to confront the photoreceptor drum. In the rotary type developing appartaus of the above described type, although the defects in the developing apparatus as disclosed in the above Japanese Patent Publications Tokkosho Nos. 55-3707 and 46-13478 may be eliminated, it is necessary to preliminarily set the developing tanks corresponding to the number of developing colors if such developing colors are to be increased in number, and thus, the size of the developing apparatus is undesirably increased on the whole as the number of colors to be used for the development is increased.
In order to overcome the disadvantages as described so far, the present inventors have previously proposed, in Japanese Patent Application Tokugansho No. 60-270314 assigned to the same assignee as in the present invention, a developing unit exchange device for a rotary type developing apparatus in which two developing units are rotatably supported for selectively causing one of the developing units to confront the photoreceptor drum, with each of a plurality of the developing units being arranged to be exchangeable.
However, in the known device as described above, if the two developing units are adapted to be rotatable regardless of respective rotating directions thereof, developing materials scattering from opening portions of the respective developing units are undesirably mixed with each other in a receiving pan, and thus, such mixed developer materials are further mixed with the developer material within the developing unit when the developing unit is being rotated. In the above case, if a non-colored developer material such as a black developer material excluding a white group developer material is mixed with the colored developer material, there arises the problem that the image quality during the development is remarkably deteriorated.